The present invention concerns a sealing device for a rolling bearing capable of maintaining a high sealing performance for a long time even under high speed rotation and high temperature circumstances.
A sealing device for a rolling bearing is disposed for preventing leakage of a lubricant sealed in the inside of the bearing and preventing intrusion of obstacles from the outside of the bearing. Particularly, in a sealing for a bearing having a worry of splash of water containing fine solids such as muddy water, for example, a bearing device used for auxiliary equipments of automobile engines. (alternators, etc.) high water proofness and dust proofness are required. Accordingly, a resilient annular sealing member is used for the sealing device and it has been adopted a structure of bringing a lip formed at the end of the sealing member into contact with a lateral side of a circumferential step (sealing groove) formed to the shoulder of a raceway groove in a rotational ring.
FIG. 1 is a cross sectional view showing the structure of an existent rolling bearing device used, for example, in an alternator. The rolling bearing comprises an inner ring (rotational ring) 1 having a side raceway groove 1u for an inner ring, an outer ring (fixed ring) 2 having a side raceway groove 2u for an outer ring, a plurality of balls 3 and a cage 4 for holding the balls 3 circumferentially each at a predetermined distance. A seal mounting groove 2x and a circumferential step (sealing groove) 1s are formed to the shoulder of the raceway groove 1u for the inner 1 ring and the shoulder of the raceway groove 2u for the outer ring 2 respectively. Further, a lubricant such as grease not illustrated is sealed in an annular space defined between the inner ring 1 and the outer ring 2, and annular seal members 5, 5 are disposed to the openings on both ends thereof for sealing the annular space.
The sealing member 5 constituting the sealing device comprises a core metal 5c made of a thin metal plate, a seal main body 5a made of rubber (or resin) formed so as to cover the core metal 5c and a lip 5b formed integrally so as to protrude to the inner circumference of the seal main body 5a. Further, the lip 5b is formed such that when the base of the seal main body 5a is fit into a seal mounting groove 2x, the top end thereof is in contact with the lateral side 1t of the circumferential step is formed to the inner ring 1.
In some bearing devices, a slinger 12 in contact with the end face of the bearing inner ring is disposed to form a labyrinth between the sealing member 5 and the slinger 12 to improve the muddy water proofness (refer to Patent Document 1 and Patent Document 2).
For the material constituting the sealing member 5, nitrile rubber, acryl rubber or the like is used generally, and materials mainly comprising a fluoro rubber or fluoro resin excellent in heat resistance and wear resistance are used suitably for bearing rotating at high speed under high temperature circumstance (for example, a highest working temperature of 170° C. or higher) such as bearings for use in alternators.    Patent Document 1            JP-A No. 10-26143            Patent Document 2            JP-A No. 2001-304280        
However, in the sealing device for a rolling bearing described above, when a fluoro resin (or fluoro rubber) is used for the material of the sealing member 5, lateral surface 1t of the circumferential step on the side of the raceway track of the bearing ring in sliding contact with the lip 5b of the sealing member is sometimes worn to lower the sealing performance in an early stage.
Further, in a case where the worn powder intrudes inside the bearing, it may be a worry of causing wear in the raceway leading to fracture of the bearing.